Factors That Affect the Nature of the Final Oxidation Products in “Peroxo‐Shunt” Reactions of Iron–Porphyrin Complexes |
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Authors: | Alicja Franke Dr Maria Wolak Dr Rudi van?Eldik Prof?Dr |
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Institution: | Department of Chemistry and Pharmacy, Egerlandstrasse 1, 91058 Erlangen (Germany), Fax: (+49)?9131‐85‐27387 |
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Abstract: | The present study focuses on the oxidation of the water‐soluble and water‐insoluble iron(III)–porphyrin complexes FeIII(TMPS)] and FeIII(TMP)] (TMPS=meso‐tetrakis(2,4,6‐trimethyl‐3‐sulfonatophenyl)porphyrinato, TMP=meso‐tetrakis(2,4,6‐trimethylphenyl)porphyrinato), respectively, by meta‐chloroperoxybenzoic acid (m‐CPBA) in aqueous methanol and aqueous acetonitrile solutions of varying acidity. With the application of a low‐temperature rapid‐scan UV/Vis spectroscopic technique, the complete spectral changes that accompany the formation and decomposition of the primary product of O? O bond cleavage in the acylperoxoiron(III)–porphyrin intermediate (P)FeIII? OOX] (P=porphyrin) were successfully recorded and characterized. The results clearly indicate that the O? O bond in m‐CPBA is heterolytically cleaved by the studied iron(III)–porphyrin complexes independent of the acidity of the reaction medium. The existence of two different oxidation products under acidic and basic conditions is suggested not to be the result of a mechanistic changeover in the mode of O? O bond cleavage on going from low to high pH values, but rather the effect of environmental changes on the actual product of the O? O bond cleavage in (P)FeIII? OOX]. The oxoiron(IV)–porphyrin cation radical formed as a primary oxidation product over the entire pH range can undergo a one‐ or two‐electron reduction depending on the selected reaction conditions. The present study provides valuable information for the interpretation and improved understanding of results obtained in product‐analysis experiments. |
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Keywords: | iron oxidation porphyrinoids peroxo ligands solvent effects UV/Vis spectroscopy |
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